Distillation of oxygenated organic compounds



May 9 H951 c. E. MORRELL ET AL. 2,551,625

DISTILLATION 0F OXYGENATED ORGANIC COMPOUNDS Filed Dec. 50, 1947 3 Sheets-Sheet 2 HYmLocAxzoNs CAREQNY 1 5 Armar-waas Esvanf,

S A109 O i5-7 fj l FEED A102 ,.FzAQTIONATOlS fw es? ALQQHQLS AQUEOUS iig Agno QTTGMS F( 1 GI.- f2

Charles E. moz/'re ZZ h* if@ Cittofnez May @a 395@ c. E. MORRELL ET AL.

DISTILLATION OF OXYGENATED ORGANIC COMPOUNDS 5 Sheets-Sheet 3 Filed DeC.

. l. nu H Y. QS L@ AI Al: f m@ 0N Il mJOOUJ @JOIGUH .LI All AXN F @ON XWON 1dOk z0rrU NEl ow i @ON :wdobazouu 0.3.. N .xml i .Tw l. l, @olli l. A wdmmzu@ 0 L. z ub. L.. @Q ..L. ...L F k e EL mdmkmm mmnwvmo n mi )ZOMU wm mMQZOU @ON modudn Charles E. Cgawl 6. Cargar. Urb/enters Patented May 8, 1951 UNITED STATES param OFFICE DISTILLATION OF OXYGENATED ORGANI-C COMPOUNDS Application December 30, 1947, Serial No. 794,589

(Cl. Zim-39.5)

9 Claims.

This invention relates to a practical method of separating wide boiling mixtures of oxygenated organic compounds and is concerned with the controlled use of water or solvents of high Water content as a reiluxing medium in a continuous fractional distillation of such wide boiling mixtures.

Wide-boiling mixtures oi oxygenated organic compounds may be -obtained for example by the Fischer synthesis in which carbon monoxide is reacted with hydrogen to produce a mixture of hydrocarbons and oxygenated Vorganic compounds which separate into an oil layer and a water layer, both of which contain various hydrocarbons, ketones, aldehydes, ethers, acetals, ketals, esters, carboxylic acids, primary, secondary and tertiary alcohols of a wide range of m-olecular weights. Still another source of these wide-boiling mixtures of oxygenated organic compounds is in the products of hydrocarbon oxidation where both oilv and water layers are obtained both of which containY oxygenated organic compounds. Atypical example of the composition of a water layer obtainedl in the Fischer process is as follows:

Weight per cent The separation of such a' complex mixture' is 'dicult to accomplish and cannot be done by ordinary distillation because of the fact that many of the compounds boil within a very .narrow range. It has been proposed previously to separate the mixture into a plurality of rnarrowboiling cuts andv then distill each of these cuts in the presence of 'a large molar excess of water, as described in copending application Serial No. 724,840, led January 28, 194'7.` However, such a .process requires a large number of 'operations to produce specification products from the original mixture.. Furthermore, `undesirable components of the original mixture iind their :way into the individual cuts causing diculty in their' 'eilicient separation. In addition, during the preliminary distillation into close-boiling cuts, chemical reactions often occur which destroy valuable components. For example, the alcohols react with ketones and aldehydes, forming ketals `andvacetals respectively. The aldehydes likewise undergo aldolization It is therefore an object of this linvention to provide a commercially feasible process for the eiiicien't separation of wide-boiling mixtures' of oxygenatedorganic compounds which are diiiicult to separate by ordinary fractional distillation methods.

It is a further object of this invention to provide a process which minimizes or prevents the loss of valuable components.

The present invention is made possible by the discovery that when a mixture of oxygenated compounds, such as those mentioned above, hare fractionally distilled in the presence of a suiciently large volume percent of aqueous reflux, the Volatilities of the oxygenated compounds are altered to such an extent that separations 'which were impossible by ordinary fractionation become possible in the presence of the excess water, and chemical reactions which occur in the absence of water are substantially prevented. The aqueous reflux used may be water or other solvents of high water content, such as aqueous solutions of salts as the chlorides, nitrates, sulfates, acetates, et cetera of sodium, potassium, ammonium and the like, dilute acids such as those obtained by distilling the crude water layer from the 'Fis- 'cher synthesis, et cetera.

VThe following table lists the relative volatility of mixtures of various oxygenated organic compounds with re'ference to ethanol at the indicated water concentrations.

Table I Volatility Relativo to Ethanol at Normal Indicated Water Concentration l Volatility Mol per cent water. n-Vuleraldchydc. n-Bntyraldchyde Methyl propyl kc Isopropanol S7 i-Butanol .3l n-Butanol. .2l n-PentanoL .09 n-Propanol.. .47 Ethanol 1. Methanol l. 7

l The relative volatility is the volatility of one component divided by that of the other, the volatility ol each component being proportional to its partial pressure divided by its incl fraction in the liquid phase. It is also defined by the equation: alpha ,1/,/1/Q`)/(I1,'xg) where y refers to the vapor phase mol fractions ol' the components to be separated and :r refers fo the liquid phase mol fractions of the components to be separate ubscript l designates thc more volatile components and subscri. 2 the less volatile components. The data in the above table indicate quito clearly that the large proportion of water present iu the liquid phase as a rcfluxing medium alters the relative volatility of the mixed organic oxygenated compounds to such an extent that separation can be easily secured.

To obtain the desired separation of puried organic components from mixtures, such as those mentioned with the benefits of the present invention, the mixture is subjected to a continuous fractional distillation in acolumn of practical size, including a rectification zone and a stripping zone for counter-current vapor-liquid contact under reboiling and reuxing conditions. A suiciently large quantity of water is introduced into an upper part of the rectification zone to effectively modify the relative volatilities of the organic compounds to be separated. The separation can be effected in a continuous manner under steady state conditions to obtain product streams of desired purities and constant compositions While supplying the large quantity of water in the upper part of the rectification zone. The temperature of the Water introduced in the rectification zone is preferably close to the temperature of the liquid on the feed plate, although it may be lowered to partially condense vapors ascending to the water feed plate.

Since the efficient separation is essentially continuous, water has to be added continuously near the top of the fractionating column while the mixture of oxygenated organic compounds to be separated is fed continuously into the column at a lower point and while sufficient heat is provided to afford distillation throughout the column.

The feed stream of the oxygenated organic compounds is preferably introduced into a fractionating column between an upper rectification section and a lower stripping section at a point where the ratio of the main organic compounds to be separated in the feed is similar to the ratio of these compounds in the internal reflux descending through the column.

The feed stream is preferably heated to a temperature close to that of the internal liquid reflux under practically equilibrium boiling conditions at the point of introduction. The preheated feed stream may be liquid, partially vaporized, or completely vaporized when introduced into the fractionation tower.

Vapors of the organic compounds introduced in the feed stream at the bottom part of the rectication zone in the fractionating column pass up the rectification zone in contact with de scending internal liquid reflux under practically equilibrium boiling and reuxing conditions.

The quantity of water required to be introduced continuously at the upper part of the rec tication zone for accomplishing the desired separation of the wide-boiling compounds is considerably greater than the quantity of condensate with which it becomes homogeneously mixed. This is necessary in order to make the water concentration of the internal reflux substantially above a, critical minimum in the range of 65 to mol per cent. With adequate water concentration in the internal reflux for effecting the separation, the organic component to be isolated in the aqueous bottoms is dissolved in the aqueous internal reux that reaches the bottom part of the rectification zone and finally the bottom of the stripping zone.

Due to the fact that water, considerably in excess of the water distilled, is introduced to mix with the condensate near the top of the rectification Zone, the water concentration in the internal reflux at the top of the rectification zone is higher than the water concentration in the vapors passing up through the zone. Contrasted therewith, in the normal rectification of oxygenated compounds from an aqueous feed, the water concentration diminishes rapidly toward the limiting water concentration of the aqueous azeotropes in the vapors ascending the fractionation tower.

The minimum water concentration in the internal reux for obtaining the separation depends on thc particular organic compounds in the original mixture. Generally essentially no separation is effected if the internal reflux contains less than 65 mol percent water; and for obtaining satisfactory results on a practical scale more than 85 mol percent of water, preferably 90 to 99 mol percent water is required in the internal reflux. As the water dilution of the internal reflux becomes infinite, the selectivity of the separation becomes increased but the efnciency is excessively lowered on account of the relatively small quantities of the organic compounds involved.

Under steady state conditions in the fractionation or distillation zone, the internal refiux having adequate water concentration for accompushing the separation of wide-boiling mixtures tends to have a nearly constant water concentration in the homogeneous liquid phase at each plate except in cases where a very dilute feed is used such as the crude water layer. In any case operation with different water concentration in the stripping and enriching zones is quite feasible. rlhis internal reux in flowing from the top to the bottom becomes richer in the components found least volatile while the other organic components of the feed become distilled overhead.

The overhead vapors from the rectification zone are enriched in one or more of the organic components rendered relatively more volatile by the high Water concentration in the liquid reflux while the remaining portion of the organic material introduced with the feed is dissolved in the internal reflux.

The functioning of the stripping zone may be described as follows:

rihe dilute aqueous solution of the wide boiling compounds to be separated, as in the liquid reiiux from the bottom of the rectification zone,

ows downwardly through the stripping zone in --countercurrent contact with v'ascending :vapors evolved l'from the solution runder relooilingzcon ditions.A A *'suzmciently. high concentration' v-of liquid. Under essentially equilibrium reboiling land reuxing conditions .in the-stripping:zone,`the

more volatile components may-.be removed as vaporoverheadffrom the stripping zone at the same rate that those components enter the stripping zone 'as part of the liquid feed to this zone and a dilute 'aqueous -solution of -the..less 4volatile components :freed from themore volatile components may be withdrawn-from the bottomrpart of the stripping zone.

'The above [principle can be applied not only .to *the crude water layer 'which is obtained lby simple separation'from thezFischer synthesisV unit but can'also be applied to oxygenated compounds recovered from the'oil .layer by aseparatefoperationinvolving-Washing ofthe oil with water or some polar solvent.f lt can also be-applied to productsrecoveredr from the recycle or'exit gases from .the synthesis I-steprby scrubbing lwith lWater ora polar compound or to mixtures'of these oxygenated compounds recovered from the oil layer yWithfthe crude water layer.

According to lone embodiment of this-invention distillation lis carried out, as described above.

under-suchconditionsthat the .overhead from `the distillation -zone consists predominantly of esters, hydrocarbons. lethers, acetals, ketals and carbonyls.' In any casethe overhead isessentially -free of lower alcohol. constituents present in the crude organic'miXture-fed tothe colmnn.

By this type of distillation it is possible to vsegregate the crude lorganic productsr-fr'om fa Fischer synthesis operation in such a vmanner lthat a mixed alcohol-acid'residue vessentially free of or greatly depleted in aldehydea ketones, esters, hydrocarbons, ketals and acetals -is obtained. The overhead besides. containingr esters, hydrocarbonsand ethers in minor amounts, will consist largely Vof yacetaldehyde, propionaldehyde,

acetone, methyl ethyl ketone; `butyra'ldehyde to- -eether with smaller amountsy of .aldehydes and ketonescontaining 5 and `6 carbon atoms.

Another embodiment ofthis invention is to so regulate operating conditions as regard heattinput) 'reflux ratio, feedrates, etc. 'toa distiliation :column of the abovedescribed-type sothat. in

addition to the carbonyls, etc., essentially a'maior portion of branched chain fand secondary and tertiary Valcohols present in the hydrocarbon synthesis Water layer are recovered overhead.

vThesebranched alcohols consistfor themost part of isopropyl and secondary and-'tertiary butyl alcohols. ylily this means it is'possible to obtain as bottoms a Water solution of acid 'together with primary alcohols of 1 to 5 carbon atomsiessentially -free of or greatly .depleted in aldehydes, ke-

tones, esters, acetals, hydrocarbons, ethers and secondary alcohols. In such an operation the key ycomponents will .probably be the lowestsecondary alcohol, namely, isopropyland Ithe `higher' primary alcohols such asnormal amyl alcohol. Under certain. conditions it may be desirable to obtain good recovery' of all the lprimaryalcohols in the bottom stream even 'if this leads to'incomplete recovery 'of the `branched `alcohols in'fthe overhead. However, it is preferred to operate so as to obtain relatively completeA removal of the 3 rbranchedfalcohols; 'especially isopropyl, Lfrom' Ithe column bottoms even atsome sacrice .infthefr'e- `covery offthe primary alcohols especially.. oCa inthe vbottoms stream. In other-words-,in-xorder to obtain complete removal of the isopropyl from :thev ethyl, it may be desirable to take loverhead :invention to the-overhead cut containing 'only l.the

neutral oxygenated` compounds. -There Iis anf ad- .vantage in this method of operation in that vthe normal butyl alcohol'and-hi'gher:

' material `-in the stripping zone visnot .diluted :with

.separation can be obtained under certain-conditions.

It is J.also possible to applyjthis .typev ofpperation to a crude aqueous solution of oXy'ger-iated .compoundsfrom the. Fischer'synthesis, Whi'chhas beenstripped before the .distillation to-:re'cover overheadas 'In-uch yas possible of 'the compounds Vmore volatile-thanthe alcohols.' In other Words, it can be applied to a-crude aqueous solution'of oxygenated compounds which has 4been previously'stripped of all` volatile Yrriaterials boiling below methyl, ethyl and isopropyl alcohols.

When operatingaccording to the lalbove'procedures, the l presenceA of large quantities 'ofrwater in the y-feed may vmake it diflicult Vtowcompletely eliminate the non-alcoholic'.constituentsfwithout taking on some of thenormal-alcohols overhead. The preliminary topping of the Ycrude water -layer `to separate the neutral-compoundsfromthe-acids helps toovercome this difficulty to some extent but complete elimination of vnormalalcohols.from the overhead cannotbe effected even :by this lexpedient if all of'ithe f-nonalcoliolic"constituents areremoved. It is -thereore'proposed .inv still-anotherembodimentof .this invention, to overcome these diiculties by rst separating the crude aqueous product from fthe -Fischer synthesis or the aciddfree -neutra=l com-pounds Vresultingy from theA above -mentioned preliminary distillation-into two fractions, one containing allcompou'nds boiling below normal butyl-alcoholr and the'other containing all lcompounds 'boil-ing inthe `rangeof Each of these .fractions is then extractively-distilled with'large quantities'otwater vas described above to remove an overhead fraction containing 'the -nonlalcoconstituents; Under "circumstances -in which it is not 4necessary to vseparate the .sec vondary and iso butyl alcohols completelyfrom therrormal alcohol-s, it'may be desirable tosoperate the vdistillation Vcolumn in such a v:manner that some or all nepropyl alcohol is :removed .in

thebottoms.

The bottoms from any' ofthe'above methodsof operation', :containingthe acids-and/orother oxy- `drmza'rbons.' also maybe' workedup in-a' variety'o'f Ways.

{tithe-accomplishment of theforegoing andere# lated ends `t ie invention then` comprises features 'hereinafter .describedl and 4particularly :pointed out in theclaims, thefollowingdescriptionizand annexed drawings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various vways in which the principle of the invention maybe employed.

Figure 1 of the drawing illustrates a flow plan of a unit for obtaining separation of a wide-boi1 ing oxygenated organic compound mixture.

Figure 2 illustrates a iiow plan of a modication of the process shown in Figure l.

Figure 3 illustrates a oW plan of a modiiication of the process shown in Figure 2.

Referring to Figure l, I represents a fractional distillation column in the interior of which is provided means for obtaining efficient countercurrent liquid vapor contact, e. g. such conventional means as bubble plates or packing and 2 represents a similar tower for separating the overhead from tower I into additional fractions while 3 and 4 represent towers for effecting better separation of the products from the bottom of towerl.

This invention will be described in detail as aD- plied to the separation of a mixture of wide-boiling oxygenated organic compounds from the total water layer obtained in the Fischer synthesis process, such a water layer having the composition given above.

Referring to the drawing, a fraction of the above composition obtained in the synthesis is introduced by line 5 into the midpoint of column I where it is fractionated in the presence of a stream of liquid water introduced through line 6. Conditions are maintained in tower I such as to cause distillation of the oxygenated compounds in the presence of the Water on each plate of the tower. A suicient amount of water is added so that it is present to the extent of 90 mol percent on each plate. As the vapors of the feed pass up the column some of them are dissolved in the large excess of water descending the column and are collected together with the water in pools on each plate. Conditions are maintained on each plate of the tower such that liquid mixtures of the oxygenated compounds are at their boiling points and are continually being contacted with vapors .boiled from the plates below. Because of the reversal of volatility in many cases many of the components which would otherwise remain in the liquid are rendered volatile. By maintaining the amount of water on each plate so large that infinite dilution is approached, the optimum relative volatilities for the separation of the desired components can be secured. Furthermore, by controlling the amount of oxygenated compounds in the reflux, the reflux ratio, and the number of plates, the actual degree of separation may be varied until the desired product purity and recovery are obtained. Accordingly, conditions are maintained so that carbonyls, esters, hydrocarbons, acetals and ethers are removed overhead as vapor.

Overhead vapors consisting essentially of carbonyls, esters, hydrocarbons (if present) and ethers are withdrawn from the top of column I through line 'I by which they are passed through condenser 8 to a receiver 9. A portion of condensate collected in receiver 9 is returned to the top part of column I as external reflux through line IU. The remaining portion of distillate collected in receiver 9 is withdrawn through line I I. This mixture is then introduced into the middle portion of tower 2 where it is subjected to normal distillation. Column 2 may be any conventional type of fractionating column such as a bubble Fischer type column or packed tower. The mixture introduced into tower 2 through line I I is subjected to fractional distillation so that acetaldehyde and any small amount of hydrocarbons present are taken overhead and withdrawn through line I2. The bottom fraction consisting of aldehydes, containing three and more carbon atoms, all ketones, esters etc. are removed from the bottom of the tower through line I3.'

Returning now to column I, bottoms liquid withdrawn from the part thereof is passed by line It. to a reboiler I5 for heating by heat exchange with a heating medium such as steam. A portion of the bottoms liquid heated and partially vaporized in reboiler I5 is recycled by line I5 to the lower part of column I. The remaining portion of the bottoms liquid is withdrawn through line I'I.

The liquid passing through line II, consisting of alcohols and acids, are passed into tower 3 where it is ,subjected to distillation to obtain a vapor fraction containing substantially all of the alcohols and a bottoms fraction containing dilute acids. The vapor fraction is withdrawn through line I8 and passed into distillation column 4 where crude methanol of good anti-freeze grade is taken out overhead through line 20. A bottoms fraction is withdrawn from tower 4 through line 2i, consisting of ethyl alcohol and higher alcohols. 'Ihis fraction may be treated in any conventional manner to separate the ethyl from the remaining alcohols. Returning now to column 3, a bottoms fraction consisting of dilute acid is withdrawn through line I9 and may be discarded. However, these dilute acids are use ful in supplying the water used as reflux to tower I. For this reason, it is preferred to recycle acid bottoms from tower 3 to tower I through line 22.

While the above description of the invention has indicated that the essential feature is that the overhead from column I is essentially free from all alcohol constituents present in the crude organic mixture fed to the column, it is an additional feature of this invention to so regulate operating conditions as regards heat input, reflux ratio, feed rates etc. in column I that in addition to the carbonyls, esters, hydrocarbons, ethers, etc. essentially a major portion of the branched, secondary and teritary alcohols present in the hydrocarbon water layer are removed overhead. These alcohols consist for the most part of isopropyl and secondary butyl alcohols. By this means it is possible to obtain as bottoms a water solution of acids together with primary alcohols of l to 5 carbon atoms essentially free of or greatly depleted in aldenydes, ketones, esters, acetals, hydrocarbons, ethers and branched, secondary and tertiary alcohols. It is particularly desirable to remove all the isopropyl from the ethyl in which case it may be desirable to remove overhead some of the normal butyl and higher normal alcohols.

Referring now to Figure 2, there is shown a modication of the invention in which the crude aqueous layer is distilled to remove overhead everything boiling below the acids and then this overhead is distilled in the presence of a large excess of aqueous reiiux.

Referring, therefore, to this drawing, a fraction having the composition used in Figure l is introduced by line E55 into column IDI where it is subjected to ordinary mstillation to remove overhead alcohols, aldehydes, ketones and esters which are withdrawn through line IBS, leaving an aqueous acid bottoms which are withdrawn 9 through. line` |01. The overhead vapors` are passedthrough condenser |108 to a receiver |99. A portion of the condensate collected in receiver |09 is returned to the top of column Iil as eX- ternal reilux through line ll. The remaining portionof the distillate collected in receiver |29l is withdrawn through line This mixture is thenintroduced into the rniddle'portion of towerl |02 whereit is fractionated in the presence of a stream; of liquid water introduced through line ||2., Conditions, are maintained in tower 32; such as to cause distillation of the oxygenated compounds in the presence of the water onv each plate of the tower. A suicient amount of water is addedso that it is present to the extent of 9,9 volume percent on each plate. The operation of column m2 is essentially the same as that of column |A in FigureV l except that due to the preliminary distillation the large volume of waterpresent in the stripping section is much less, thus resulting in better separation over-hea 'lhus thefoverhead vapors from tower |92 consist oi carbonyls, esters, hydrocarbons (if present) and` ethers. These are withdrawn through line H3, condensed in cooler |11 and collected in receiver I5..i vA portion ofl thematerial in receiver ||5 is passed by line l I6 to the top of tower W2 as ,external reiiux.y The remainder is withdrawn through` line. I|l for furtherl separation, if desired,

The aqueous alcohols are withdrawn from the loottonrof` tower HB2r through line i i8 for further separation as desired.

If ldesired a portion of the aqueous acid bot toms `v vithrdravfsn through line it? may be passed z,

through line H9 and7 used as the aqueous. reflux introduced through line H2.

As `mentioned in connection with tower i of FigureV l, tower |62 may be operated so that a major .portion of the branchedsecondary and tertiary alcohols are removed overhead together withv VtheA carbonyls, esters, hydrocarbons and @there Referring now to Figure 3, there is shown an additional modification, of the invention shown in Figure'Zfin which the overhead from the'preliminary distillation of the crude water layer is.

separated into two fractions, one boiling below and the other boiling above normal propyl alcohol and in which each of these fractions is distilled in the presence of a large excess of an aqueous reflux.

Referring, therefore, to this drawing, the;over head from thepreliminary fractionation zone I li obtained as described in connection with Figure 2, is passed by line il! to a second fractionation zone 262 where it is subjected to ordinary fractionation to take overhead methylalcohol, acetone, acetaldehyde, dimethyl acetal, ethyl ketone, propionaldehyde, butyraldehyde, ethylalcohol, normal and isopropyl alcohol, ethyl acetate, diethyl acetal, secondary butanol,v isobutanol', tertiary butanol, isopropyl acetate, normalpropyl acetate, methyl normal propyl ketone, methyl isopropyl ketone, diethylketone, methyl isobutyl ketone, ethyl propionate, normal and iso-valeraldehyde, methyl normal butyl ketone andY light hydrocarbons. The bottoms fraction will contain in addition to n-butyl alcohol all the constituents boiling above normal butyl alcohol. Depending upon the exact degree of con trol effected. and the importance of freeing the higher Vnormal alcohols of secondary and isobutyl alcohols, some. n-propyl alcohol, secondaryand isobutyl alcohols will be taken asbottoms. The

methyl overhead fraction is passed by line 263 to the midle portion of tower 291i where it is fractionated in the presence of a stream of liquid water introduced through line 2535. Conditions are maintained in tower 29d similar to those maintained in tower |92 of Figure 2 so as to cause distillation of the oxygenated compounds in the presence of the water on each plate of the tower. A sufficient amount of water is added so that it is present to the extentof 9 0 volumeV percent on each plate and conditions are maintained so that the non-alooholic constituents present in the fraction fed to the tower are taken overhead. Thus acetone, acetaldehyde, dimethyl acetal, methyl ethyl ketone, propionaldehyde, butyraldehyde, ethylacetate and diethyl acetal, isopropyl l acetate, n-propyl acetate, methyl-npropyl ketone, methyl isopropyl ketone, diethyl ketone, methyl isobutyl ketone, methyl-n-butyl ketone, ethyl propionate, normal and iso-valeraldehyde are present in the overhead fraction leaving a solution of alcohols in the bottom.`

Returning now to column 2t2, the bottoms fraction containing in addition to n-butyl alcohol all constituentsboiling above normal butyl alcohol, any normal propyl and secondary and isobutyl alcohols and tertiary amyl alcohol not taken overhead, is passed by line 2% to the midpoint of tower 29'! where it is subjected to fractionation in the presence of a stream of liquid water introduced through line 298, so that the water is present tothe extent of 90 volume percent on each plate. The operation of tower 2li? is the same as that of 29d whereby the non-alcoholic ketones, aldehydes, esters, ketals, acetals and any hydrocarbons present are taken oi overhead through line 259 and an aqueous solutionof alcohols are removed from the bottom through line 2id.

A suitable source of aqueous reflux for towers i 2stand Zelf is the dilute acids removed from the passed by lines 21| and Zit and introduced into the topvof tower 2.6ithrough line 298.

Example I A sample oi a water layer from a Fischer synthesis containing 84.6 mol percent of alcohols, 11.2 mol percent of carbonyls (ketones and aldehydes), 0.2 mol percentof esters and 4.() percent of acids on a water-free basis was distilled in a oneinch I. D. perforated platercolumn having 30 plates above and 30 plates below the feed point at .a feed rate of 485 c. c. per hour, while introducing water as reflux at the top of the column at a rate of 945 c. c. per hour so that the top plate of the columncontained 98 lmol percent water. The feed` was introduced at a temperature of 91- C. and the water at 94 C. The overhead temperature was-maintained at 84 C. and the reflux ratio at 15:1. .A total of 6.2% of organic materialk based on the feed and consistingV ofl ketones, aldehydes, esters .and only a small amount. or" alcohols was removed overhead. A bottoms. fraction consisting of an aqueous solution of alcohols and acids was withdrawn and passed toa second distillation zone similar to the rst at arate of i310 c. c. per hour and a temperature of 91 C. The reux ratio of the second tower was 5:1. Alcohols were removed overhead at a temperature of 79 C. A solution of acids in water. wereremoved from the bottom .and re- 1l turned to the top of the first column as reux therein. The following data were obtained.

l Ol' exi-motive distillation column.

Example II A sample of the water layer used in Example I was distilled in the same manner as in Example I except that the amount of water added was decreased to 930 c. c. per hour to maintain 96.8 mol percent water on the top plate, the feed rate to the first distillation zone was lowered t 440 c. c. per hour, the anhydrous overhead rate was increased to 8.4 c. c. per hour. By operating in this manner, 19.1 volume percent of the organic matter in the feed was taken overhead, including most of the branched secondary and tertiary alcohols. The following table illustrates the results obtained:

l Of extractive distillation column.

The above data indicate clearly that the undesired impurities present in the water layer of a product from the Fischer synthesis can be adequately removed by distilling the water layer in presence of a large excess of aqueous reflux.

While one specific process involving the novel steps of the present invention as well as one specic apparatus for carrying out the same has been described in detail, it is to be understood that this description is illustrative only and for the purpose of making the invention clearer, and it is not intended that the invention shall be construed as limited to details of the description except insofar as such limitations have been included in the terms of the following claims.

The nature and obj eots of the present invention having been set forth and specic illustrations of the same given, what is claimed as new and useful and desired to be secured by Letters Patent is:

l. The method of separating a mixture of aqueous oxygenated organic compounds containing at least two normal primary alcohols, branched alcohols and neutral non-alcoholic oxygenated compoundsI in the C1 to C5 molecular weight range `which comprises continuously introducing said mixture into an intermediate point of a fractionation zone, continuously adding suiiicient water to the fractionation zone at a point substantially above the mixture feed point to maintain an internal liquid reflux having a water content in the range of 65 to 99 mol per cent below the point of addition of the water, distilling from the mixture vapors of the oxygenated compounds which ow countercurrent to the aqueous reflux, removing overhead from the fractionation zone an aqueous distillate consisting of neutral nonalcoholic oxygenated compounds and recovering as bottoms from the fractionation zone an aqueous solution consisting of the normal primary and branched alcohols.

2. The method of separating a mixture of aqueous oxygenated organic compounds containing at least two normal primary alcohols, branched a1- cohols, neutral non-alcoholic oxygenated compounds and acids in the C1 to C5 molecular weight range which comprises continuously introducing said mixture into an intermediate point of a fractionation Zone, continuously adding sufcient water to the fractionation zone at a point substantially above the mixture feed point to maintain an internal liquid reflux having a water content in the range of to 99 m01 per cent below the point of addition of the water, distilling from the mixture vapors of the oxygenated compounds which flow countercurrent to the aqueous reflux, removing overhead from the fractionation zone an aqueous distillate consisting of the neutral non-alcoholic oxygenated compounds and recovering as bottoms from the fractionation zone an aqueous solution consisting of the normal primary and branched alcohols and acids.

3. A process according to `claim 2 in which the aqueous solution recovered from the fractionation zone is fractionated in a second fractionation zone to produce an overhead distillate of alcohols and a bottoms of aqueous acid which is recycled as water reflux to the first fractionation zone.

4. The method of separating a mixture of aqueous oxygenated organic compounds containing at least two normal primary alcohols, branched alcohols, neutral non-alcoholic oxygenated compounds and acids in the C1 to C5 molecular weight range which comprises introducing the mixture into a rst fractionation zone, removing overhead from the rst fractionation zone a distillate comprising substantially all of the neutral nonalcoholic oxygenated compounds and al1 the alcohols, removing a bottoms product from the first fractionation zone comprising substantially aqueous acids, introducing the distillate from the rst fractionation zone into an intermediate point of a second fractionation zone, continuously adding suicient aqueous acid bottoms from the first fractionation zone to the second fractionation zone at a point substantially above the distillate feed point to maintain an internal liquid reflux having a water content in the range of 65 to 99 mol per cent below the point of addition of the aqueous acid bottoms distilling from the mixture vapors of the oxygenated compounds which now countercurrent to the aqueous acid reflux, removing overhead from the second fractionation zone a distillate consisting of the neutral non-alcoholic oxygenated ycompounds and recovering as bottoms from the second fractionation zone an aqueous solution consisting of the normal primary and branched alcohols and acids.

5. The method of separating a mixture of aqueous oxygenated organic compounds containing at least two normal primary alcohols, branched alcohols, neutral non-alcoholic oxygenated compounds and acids in the C1 to C5 molecular weight range which comprises introducing said mixture into a rst fractionation zone, removing overhead from said rst fractionation zone the alcohols and the neutral non-alcoholic oxygenated compounds, recovering bottoms from the first fractionation zone comprising an aqueous solution of the acids, introducing the overhead from the first fractionation Zone into an intermediate point of the second fractionation zone fractionating said overhead in the second fractionation 13 zone to obtain a distillate comprising all compounds boiling Within the range of the normal alcohols having A carbon Vatoms, per molecule and a bottoms fraction comprising all compounds boiling `Within the range of normal alcohols having B carbon atoms per molecule, passing the A fraction into an intermediate section of a third fractionation zone, passing the B fraction into an intermediate section of a fourth fractionation zone, continuously adding water to said third and fourth fractionation zones at a point substantially above the respective feed points thereof to maintain an internal liquid reux having a water content in the range of 65 to 99 mol per cent below the point of addition of the Water, removing overhead from the third and fourth fractionation zones an aqueous solution consisting of the neutral non-alcoholic oxygenated compounds having A carbon atoms per molecule and neutral nonalcoholic oxygenated compounds having B carbon atoms per molecule respectively and recovering as bottoms from the third and fourth fractionation Zones an aqueous solution consisting of the alcohols having A carbon atoms per molecule, and alcohols having B carbon atoms per molecule respectively.

6. A process according to claim 5 in which the aqueous internal reflux to the third and fourth fractionation zones is provided by introducing thereto the aqueous acid -bottoms derived from the rst fractionation zone.

7. A process according to claim 5 in which A is l to 3 and B is 4-5 respectively.

8. A process according to claim 5 in which A is 1 to 2 and B is 3-5 respectively.

9. A process according to claim 6 in which A is Ci-Ca and B is Ca-C5 respectively.

CHARLES E. MORRELL. CARL S. CARLSON. PAUL V. SMITH, JR.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 996,328 Guillaume June 27, 1911 1,929,901 Ricard et al Oct. 10, 1933 1,933,505 Merley Oct. 31, 1933 2,179,991 Bright et al Nov. 14, 1934 2,198,651 Bludworth Apr. 30, 1940 2,283,911 Brant et al. May 26, 1942 2,290,442 Metzl July 2l, 1942 2,290,636 Deanesly July 21, 1942 2,324,755 Beamer July 20, 1943 2,364,341 Bright et al Dec. 5, 1944 

1. THE METHOD OF SEPARATING A MIXTURE OF AQUEOUS OXYGENATED ORGANIC COMPOUNDS CONTAINING AT LEAST TWO NORMAL PRIMARY ALCOHOLS, BRANCHED ALCOHOLS AND NEUTRAL NON-ALCOHOLS, BRANCHED ALCOMPOUNDS IN THE C1 TO C5 MOLECULAR WEIGHT RANGE WHICH COMPRISES CONTINUOUSLY INTRODUCING SAID MIXTURE INTO AN INTERMEDIATE POINT OF A FRACTIONATION ZONE, CONTINUOUSLY ADDING SUFFICIENT WATER TO THE FRACTIONATION ZONE AT A POINT SUBSTANTIALLY ABOVE THE MIXTURE FEED POINT TO MAINTAIN AN INTERNAL LIQUID REFLUX HAVING A WATER CONTENT IN THE RANGE OF 65 TO 99 MOL PER CENT BELOW THE POINT OF ADDITION OF THE WATER, DISTILLING FROM THE MIXTURE VAPORS OF THE OXYGENATED COMPOUNDS WHICH FLOW COUNTERCURRENT TO THE AQUEOUS REFLUX, REMOVING OVERHEAD FROM THE FRACTIONATION ZONE AN AQUEOUS DISTILLATE CONSISTING OF NEUTRAL NONALCOHOLIC OXYGENATED COMPOUNDS AND RECOVERING AS BOTTOMS FROM THE FRACTIONATION ZONE AN AQUEOUS SOLUTION CONSISTING OF THE NORMAL PRIMARY AND BRANCHED ALCOHOLS. 